A potassium titanate is useful as a friction material for forming a friction sliding member (e.g., brake lining, disc pad, and clutch facing) that is included in a braking device used for automobiles, railroad vehicles, airplanes, industrial machines, and the like. A potassium titanate is represented by the general formula: K2O.nTiO2 (wherein n is an integer from 1 to 12). In particular, potassium hexatitanate represented by K2O.6TiO2 (n=6) has a tunnel crystal structure, and it has been known that a friction material that includes fibrous potassium hexatitanate (fibrous potassium hexatitanate particles) exhibits excellent heat resistance and the like.
However, a fibrous potassium titanate is bulky, and exhibits inferior formability. Moreover, it is difficult to uniformly disperse a fibrous potassium titanate in a friction material due to low fluidity (i.e., a fibrous potassium titanate is difficult to handle).
Patent Document 1 (JP-A-4-280815) discloses a method that produces a particulate potassium titanate (instead of a fibrous potassium titanate) by pouring a titanium tetrachloride aqueous solution into an aqueous solution of a dibasic or tribasic carboxylic acid (e.g., oxalic acid) (that is heated to 50° C. or more), filtering the resulting hydrous titanium dioxide-organic acid condensate, followed by washing with water to obtain an aqueous suspension, adding potassium hydroxide to the aqueous suspension, and reacting the mixture at a temperature of 50° C. or more and a pH of 8 or more, followed by filtration, washing with water, and drying.
It is normally desirable that a potassium titanate powder used for a friction material have a specific surface area of 5 to 10 m2/g. However, since the potassium titanate powder disclosed in Patent Document 1 has a specific surface area as large as 100 m2/g or more, it is difficult to sufficiently improve friction properties.
A method that mixes a titanium compound and a potassium compound, and calcines the mixture to produce a rod-like or columnar potassium titanate (instead of a fibrous potassium titanate) has been studied. According to this method, however, it is difficult to suppress the growth of potassium titanate crystals in the longitudinal direction (major axis direction), and a considerable amount of fibrous potassium titanate is included in the product. Moreover, since it is necessary to perform a component adjustment process (e.g., pH adjustment or washing with an acid) after calcination, it is impossible to easily produce the desired potassium titanate.